Arc spraying torches have been used in order to melt a spray material having wear resistance or other properties by an electric discharge arc, spray the molten spray material on a surface of a metal as a substrate for deposition, and improve wear resistance and other properties of the metal. Such an arc spraying torch is configured such that a pair of wire-like or bar-like flexible spray materials are guided by a pair of spray material guides to bring tips of the spray materials close together in a melting area to cause an arc between the tips and melt the spray materials by the arc, and the molten spray materials are jetted on the metal surface by an air jet for deposition. The arc spraying torch includes a spraying head having a head at one end of a long stem and an operation unit at the other end, and allows spraying on a spot where it is impossible to spray by other melting spraying methods.
As shown in FIGS. 1 to 3, a conventional arc spraying torch having a long stem includes an operation unit c attached to one end (a right end in FIG. 1) of a stem b of an arc spraying torch a, and a head d attached to the other end. The head d includes a pair of spray material guides f attached to a front wall of a head body e so as to protrude forward, and a nozzle g that is attached between the spray material guides f so as to protrude forward from the front wall and jet forward jet air, a pair of wire-like spray materials m having been taken in from a rear portion of the operation unit c, and fed by a feed mechanism in the head through the stem are inserted into corresponding spray material guides and fed out from the tips thereof; the spray materials are energized via an unshown energized electrode for discharge between the tips of the spray materials, molten by a discharge arc and then deposited on a desired metal surface by the jet air.
Another conventional arc spraying torch having a long stem includes a stem and a head aligned with each other as the above described example, and as shown in FIG. 4, a nozzle j of the head h is attached to a head body 1 away from a surface including a pair of spray material guides k (on an upper side in FIG. 4), and a molten spray material is sprayed longitudinally of the stem, thus substantially perpendicularly to an axis of the head for deposition.
However, in the former conventional arc spraying torch, a jet direction of the jet air from the nozzle g is the same as an axial direction of the stem b, and for example, the jet direction of the spray material is tilted and slightly angled with respect to a surface to be sprayed, that is, a work surface in a narrow spot where it is hard to externally spray such as an inside of a passage of a Francis turbine runner, thus the spray material cannot be appropriately deposited on the work surface. In the latter conventional arc spraying torch, the air is applied perpendicularly to a feeding direction of the spray material, and thus there are problems in quality such as a low acceleration speed of particles of the molten spray material, uneven sizes of the particles, resultant low adhesion of a film to a substrate, weak bonding between the particles, lack of density of the film, and high porosity. The film n of the spray material deposited on the substrate p may be thicker on one side as shown in FIG. 5.
These conventional arc spraying torches have to be actually used as an arc spraying method for an inner surface at the expense of the quality of the film, therefore, an improved arc spraying torch is desired.